The present invention relates to a nickel or nickel alloy sputtering target superior in film uniformity (evenness of film thickness) and plasma ignition (firing) performance, and the manufacturing method thereof.
The sputtering method is widely used as the method for forming a magnetic thin film on the likes of a hard disk magnetic recording medium, magnetic head, LSI chip and so on.
This sputtering method makes a positive electrode target and a negative electrode target face each other, and generates an electric field by applying a high voltage between the substrates thereof and the targets under an inert gas atmosphere. The sputtering method employs a fundamental principle where plasma is formed pursuant to the collision of electrons, which are ionized at such time, and the inert gas, the positive ion in this plasma extrudes the atoms structuring the target by colliding with the target surface, and the extruded atoms adhere to the opposing substrate surface, wherein the film is formed thereby.
For most of the sputtering performed today, a method referred to as magnetron sputtering is employed. This magnetron sputtering method sets a magnet on the back side of the target, and generates a magnetic field in the perpendicular direction with the electric field on the target surface in order to perform sputtering. As a result, enabled is the stabilization and high purification of plasma in such a perpendicular magnetic field space, and there is an advantage in that the sputtering speed can be increased.
Generally, this type of magnetron sputtering method is employed for forming on a substrate a magnetic thin film such as a ferromagnetic body or ferromagnetic body formed from Ni, Co or the like. Although the magnetron sputtering method is able to capture electrons within the magnetic field and efficiently ionize the sputtering gas, when the target is magnetic, the target itself affects the magnetic field in the vicinity of the sputtering face with its magnetic properties.
In recent years, particularly as the gate material, the use of nickel or nickel alloy has been proposed in place of cobalt since it possesses characteristics of having a low silicide forming temperature, electrical resistance of the film being low, silicon used in the silicide reaction being small, and so on.
In general, there is a problem in that it is extremely difficult to perform magnetron sputtering to a ferromagnetic body for magnetically creating a closed circuit. Nevertheless, recently, a ferromagnetic target formed from nickel or nickel alloy is also able to obtain sufficient deposition rate so as long as the thickness of the nickel or nickel alloy target is roughly 5 mm due to the improvement in the magnetron sputtering device employing the likes of a powerful magnet.
Nonetheless, to put it in other words, with a target formed from nickel or nickel alloy, there is a significant task of processing the target to obtain a thin and even film having thickness of 5 mm or less, preferably 3 mm or less.
Further, when employing a target having uneven magnetic properties within the sputtering face, the deepest part of the erosion portion will become strained, and there is a problem in that the scheduled film thickness distribution cannot be obtained. It could be said that a nickel or nickel alloy target, which is magnetic, particularly shows this kind of tendency.
With a flat rolled target material, the strain is not isotropic as a matter of course. In other words, it becomes an aggregate structure in which crystal grains are extended in one direction. Therefore, when viewing this three dimensionally, and even within the rolling face, anisotropy will arise in the magnetic properties.
Although a nickel or nickel alloy target employs magnetic anisotropy, it has a drawback in that strain or the like exists as is in the internal structure.
When cutting a discoid target from this kind of rolled sheet and preparing a target, the portion where erosion should progress by nature will be extended in one direction.
Fundamentally, upon performing deposition on a circular substrate, it was expected that the erosion portion would be circular by nature, and there is a problem in that an even film thickness could not be obtained on such a circular substrate.
In light of the above, since the thickness of deposition usually affects the magnetic properties, it is necessary to obtain a certain degree of film thickness and which is even. Nevertheless, the gate film may be thin, and the deposition rate and film thickness do not usually cause any problems.
In the foregoing deposition characteristics, however, the film uniformity (evenness of film thickness) significantly influences the properties of the gate film, and, in particular, this is becoming a major problem in the recent 300 mm wafer process.